Method for treating myopia with an aspheric corneal contact lens

ABSTRACT

Aspheric corneal contact lenses are used to treat myopia by controlled corneal molding. In one embodiment of the method, the lens includes an asymmetric central zone which provides multiple focusing capability to correct both near and far vision. A tear zone is located concentrically around the central zone. The tear zone is integral with the central zone and has a radius of curvature which is smaller than the central zone. The lens also includes a peripheral zone located concentrically around the tear zone wherein the peripheral zone has a radius of curvature equal to or greater than the central zone.

This is a continuation-in-part of my patent application Ser. No.08/009,322 which was filed on Jan. 26, 1993, now U.S. Pat. No.5,349,395, and which was a continuation-in-part of Ser. No. 07/748,845which was filed on Aug. 23, 1991, now U.S. Pat. No. 5,191,365.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to corneal contact lenses andtheir use in treating myopia. More particularly, the present inventionis directed to corneal contact lenses which are shaped to providegradual altering of the patient's cornea during continued wear toreshape the cornea to reduce the myopic condition.

2. Description of Related Art

Myopia, also known as nearsightedness, is a condition where the radiusof curvature of the cornea is smaller than normal. Individuals with thiscondition have difficulty in focusing on distant objects because thecornea the curved too sharply to provide adequate focusing. Myopia is acommon condition for which no entirely suitable permanent treatment hasbeen developed.

One approach to correcting myopia is through surgical reshaping of thecornea. However, such surgical procedures have not been entirely provenand there is some question as to the permanency of the surgicallyaltered lens shape.

Another approach is to alter the corneal shape by wearing cornealcontact lenses which are designed to continually exert pressure onselected locations of the cornea to gradually force or mold the corneainto the desired normal corneal curvature. A retainer lens is then wornon a part time basis to prevent the cornea from returning to itsoriginal shape. This method of treatment is commonly referred to asorthokeratology. The success of any treatment by orthokeratology isdependent upon the shape and structure of the corneal contact lens.

My prior U.S. Pat. No. 4,952,045 discloses a contact lens which isspecifically designed for use in treating myopia. The lens includes acentral zone, a tear zone located concentrically around the central zoneand an outer peripheral zone which is located concentrically around thetear zone. This lens is designed specifically so that the radius ofcurvature of the tear zone is smaller than the radius of curvature forboth the central zone and peripheral zone. I discovered that thiscorneal lens configuration is useful in changing the shape of the myopiccornea to that of a normally shaped cornea. In addition, the sharpercurve of the tear zone provides a ring-shaped area where tear fluid isconcentrated between the lens and cornea.

Although the corneal contact lens disclosed in U.S. Pat. No. 4,952,045is well-suited for its intended purpose, there is continual need forimprovement of the design of such a lens to make it better suited foruse in treating myopia. For example, in many situations myopic patientsrequire a multiple focus lens, such as a bifocal lens, to provideadequate near and far vision. It would be desirable to provide suchpeople with a multiple focus lens which also includes the features of myprior lens.

SUMMARY OF THE INVENTION

In accordance with the present invention, a corneal contact lens fortreating myopia is disclosed wherein the lens is a multiple focal lenswhich is designed for patients requiring both near and far visioncorrection. The lens of the present invention is based upon the lensdisclosed in U.S. Pat. No. 4,952,045 wherein the corneal contact lensincludes a central zone and a tear zone having a radius of curvaturewhich is smaller than that of the central zone. The present inventioninvolves shaping the central zone so as to form an aspheric portion ofthe lens which provides a multiple focus or correction zone. As afeature of the present invention, the aspheric shape of the multiplefocus zone provides bifocal correction for both near and far vision.

As another feature of the present invention, the central zone isaspherically shaped and the relative diameter of the central zone isincreased with respect to the tear zone and the outer peripheral zone.This increases the visual zone to provide multiple focusing over alarger area to enhance visual correction.

As a further feature of the present invention, a method of treatment isdisclosed wherein an aspherically shaped lens, with or without the tearreservoir, is used to gradually reshape the myopic eye to provide normalvision. Once vision is corrected as much as possible, the asphericallyshaped lens is used as a retainer to prevent the cornea from returningto its myopic state. The lens also may be worn initially as a retainerlens to help prevent the development of myopia.

The above described and many other features and attendant advantages ofthe present invention will become better understood by reference to thefollowing detailed description when viewed in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a rear view of a preferred exemplary corneal contact lenswhich is suitable for use in the method of the present asphericinvention.

FIG. 2 is a sectional side view of the lens shown in FIG. 1.

FIG. 3 is a rear view of a preferred exemplary lens which is suitablefor use in the method of the present invention.

FIG. 4 is a sectional side view of the lens shown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS

The present invention is an improvement upon my prior U.S. Pat. No.4,952,045. The contents of my prior patent is hereby incorporated byreference.

A preferred exemplary corneal contact lens in accordance with thepresent invention is shown generally at 10 in FIGS. 1 and 2. The lens 10includes a central portion or zone 12, a tear portion or zone 14 and aperipheral portion or zone 16. The overall dimension of the lens 10 arewithin the normal ranges for corneal contact lenses. The outsidediameter of the lens is typically between about 5 to 20 millimeters withother diameters being possible in special cases. In general, most lenseswill have overall diameters in the neighborhood of 10 millimeters.

The lens has an anterior surface 18 which is shaped in the same manneras conventional contact lenses. The anterior surface 20 is shaped toprovide the central zone 12, tear zone 14 and peripheral zone 16 as willbe described in detail below. The lateral thickness of the lens 10 willvary since the anterior surface curve 18 does not have to match thevarious curves of the posterior surface 20. The lateral thickness of thelens will vary depending upon a number of factors including thecorrective prescription of the lens and the overall diameter. Therelationship between lens thickness and the lens prescription are wellknown by those skilled in the art.

In accordance with the present invention, the curve of the posteriorsurface 20 in the central zone 12 is aspheric and produces an asphericcentral zone 12 which provides multiple focusing of light as it passesthrough the lens and into the wearers eye. The eccentricity of theaspheric curve is between 0.04 to 1.5. Eccentricities on the order ofabout 0.10 to 1.0 are preferred.

The posterior surface of the central zone 12 has a radius of curvaturewhich gradually increases from a minimum of 4 millimeters to a maximumof 20 millimeters as one moves from the center of the central zone 12 tothe perimeter of the zone. The anterior surface of the central zone 12has a radius of curvature which may or may not match the radius ofcurvature of the posterior 20, i.e. the anterior surface may be sphericor aspheric if desired. The central zone 12 of the lens is aspheric asshown in FIG. 2 and provides multiple focal points. In addition, thecentral zone 12 has a diameter which is maximized to enhance thecorrection of vision provided by the multiple focal points. Diameters onthe order of about 6 to 20 millimeters are preferred with 9 to 12millimeters being most preferred.

The tear zone 14 forms a ring around the optical zone 12 and is integraltherewith. The chord length of the tear or intermediate zone 14 isbetween about 0.1 to 2 millimeters. The radius of curvature of the tearzone 14 is between about 0.1 to 12 millimeters. The preferred ranges arefrom 0.2 to 3 millimeters for the chord length and 6 to 9 millimetersfor the radius of curvature. The radius of curvature may be spherical oraspheric. Aspheric curves are preferred for the tear zone 14 with therange of eccentricities being on the order of -1.0.

As disclosed in detail in my prior U.S. Pat. No. 4,952,045, an importantfeature is that the radius of curvature of the tear zone 14 must besmaller than the radius of curvature for the central zone 12. Thiscreates a zone of increased curvature around the central zone 12 whichprovides desirable reshaping of the cornea. In addition, a circular tearchannel or duct is formed between the tear zone 14 and the eye toprovide a concentrated zone or reservoir of tear fluid which helpsposition the lens carefully on the cornea and enhances lens wearingcomfort. Preferably, the radius of curvature of the tear zone will bebetween 0.5 millimeter and 1.0 millimeter less than the smallest radiusof curvature of the central zone 12.

The peripheral zone 16 is integral with the remainder of the lens inthat it is preferably machined or molded from the same piece of polymermaterial. The peripheral zone 16 has a radius of curvature of betweenabout 0.4 to 20 millimeters. The radius of curvature may be spheric oraspheric. Eccentricities on the order of about 1 to 2 are preferred. Thechord length of the ring defined by the peripheral zone 16 is betweenabout 0.1 to 2 millimeters. The preferred ranges are 8 to 15 millimetersfor the radius of curvature and 0.1 to 1.0 millimeter for the chordlength.

The posterior surface of the peripheral zone 16 may have a single radiusof curvature or it may be divided into a plurality of smaller peripheralcurves. The radii of curvature of the plurality of peripheral curves maybe gradually increased from the radially inward curve to the radiallyoutermost curve. Preferably, the innermost peripheral curve will have aradius of curvature slightly above the radius of curvature for the tearzone 14. The outermost peripheral curve will preferably have the largestradius of curvature. However, the radius of curvature may be varied forspecific designs and treatments, if desired.

The chord length or optical zone for each of the peripheral curves ispreferably between about 0.05 millimeter and 0.1 millimeter. The numberof peripheral curves present can be varied if desired; however, it ispreferred that multiple curves or total aspheric edge lift be providedin the peripheral zone 16. In addition, the chord length of each of theperipheral curves may be varied. Alternatively, the innermost peripheralcurve and outermost peripheral curve may have chord lengths which arelonger than the peripheral curves located therebetween. The number ofperipheral curves in the posterior surface can be increased to provide acontinuous aspheric peripheral zone in which the radius of curvaturegradually increases towards the outer radial edge of the lens in thesame manner as the central zone.

The lens 10 can be made according to any of the known machining ormolding processes which allow variable radii of curvature lenses to beformed. The preferred procedure is to machine the lens from buttons ordisks as is commonly known. The materials used in making the lens 10 canbe any of the conventional polymers used in hard, semi-hard and softhydrogel corneal contact lenses. These materials include a variety ofsilicone and fluorine substituted acrylates, styrene and the softhydrogel or silicone lens materials used in oxygen permeable contactlenses. If desired, the three zones 12, 14, and 16 can be made from thesame lens material or different lens materials. For example, a suitablelens 10 could include a hard plastic central zone 12 and peripheral zone16 while having a semi-hard or soft tear zone 14. Additional controlover corneal reshaping or molding is provided by this ability to varythe hardness of the individual zones.

As an example, a preferred exemplary lens has an overall diameter of 11millimeters and a high DK value (e.g. on the order of 500). The centralzone 12 has a diameter of 7.8 millimeters. The radius of curvature forthe anterior surface of the central zone 12 is 8.00. The eccentricity is1.0 and the prescription is -2.00. The tear zone 14 has an optical zoneor chord length which is 1.0 millimeters long and a posterior surfacewith a radius of curvature of 7.30 millimeters. The eccentricity of thetear zone posterior surface is -1.0. The peripheral zone 16 has andoptical zone or chord length which is 0.6 millimeter long and a radiusof curvature for the posterior surface of 11.0 millimeters. The radiusof curvature for the anterior surfaces of the lens are matched to theposterior surfaces. The exemplary lens provides bifocal vision with acorrection of about +1.5.

The method of the present invention involves gradually reshaping themyopic cornea with a series of aspherically shaped lenses over a periodof time. The method has been found to be effective in treating myopia ofup to 15 D (diopters) and higher. The gradual reshaping of the corneacan take from a few weeks up to a year or more depending upon theseverity of the myopia. In general, it will take a few months and from 3to 7 lenses to achieve desired levels of cornea shaping.

In accordance with the method of the present invention, the eye to betreated is measured to determine the CK (corneal keratometer) readingand the TK (temporal keratometer) reading. The first aspheric lens inthe series is designed to provide a maximum central touch fitting. Acentral touch fitting of the lens is designed to apply pressure to thecentral area of the cornea, i.e. the lens touches the cornea more in thecenter than in the peripheral areas. Preferred central touch fittingprovides for from 1 to 3 millimeters of contact between the centerportion of the lens and the cornea. In general, the maximum amount ofcontact between the center of the lens and the cornea is preferredprovided that such contact does not adversely affect other fittingfeatures.

Central touch fitting is also known as apical touch fitting and isdesigned to promote a more spherically shaped cornea. Central touchfitting is a term known in the art by optometrists, ophthalmologists andother skilled workers involved in fitting patients with contact lenses.

The optimum central touch for the first aspheric lens in the series isdetermined by routine experimentation. The CK and TK readings for thepatient are taken and a lens with an estimated good central touch isprepared. A few lenses having prescriptions on either side of theestimated optimum central touch lens are also prepared. The group oflens are then fitted to the patient to determine which lens provides theoptimum central touch. It was discovered that the central pressurecaused by the lens with a central touch fit is sufficient to causegradual flattening of the cornea. After 1 to 2 weeks, the cornea is thenchecked for reshaping, i.e. flattening. If the cornea has flattened, anew lens is again central touch fit. In general, the next lens in theseries is not prescribed until a change in optimum central touch fittingof from 0.5 to 1.0 diopters has been obtain.

Depending upon patient progress, the eye is measured at weekly, biweeklyor monthly intervals to determine reshaping progress. New asphericlenses are central touch fit as necessary until the cornea is withinnormal diopter limits.

After the cornea has reached the desired shape, the last aspheric lenswhich was central touch fit is prescribed for continued wear as aretainer to prevent the cornea from gradually returning to its myopicstate. In some cases, the cornea is within normal limits and does notneed to be reshaped. In these cases, the aspheric lens is central touchfit and worn as a retainer lens to prevent the cornea from losing itsshape and becoming myopic.

The lens shown in FIGS. 1 and 2 is suitable for use in the methoddescribed above. Aspheric lenses, such as the lens shown in FIGS. 3 and4, may also be used. This lens, which is shown generally at 30, has thesame basic aspheric shape as the lens shown in FIGS. 1 and 2 except thatthere is no well-defined central zone, tear zone or peripheral zone.Instead, the lens 30 has a posterior surface 32 having a continuousaspheric curve as best shown in FIG. 4. The aspheric curve of theposterior surface may have an eccentricity of between about 0.6 to 1.0.Eccentricities of about 0.7 to 0.8 are preferred to provide optimumcomfort while still providing multifocal vision correction and myopiacorrection.

The anterior surface 34 of lens 30 may be aspheric to match the shape ofthe posterior surface 32 or it may be changed slightly to provideadditional vision if desired.

A study was conducted to demonstrate the effectiveness of the asphericlens when used in accordance with the method of the present invention.The study was conducted on 200 eyes (100 patients) over a 3 monthperiod. The lenses used had the shape shown in FIGS. 3 and 4. The lenseswere all made from a fluorine acrylate gas permeable plastic.

The patient criteria was: myopia up to 10 D (diopters); keratometerreadings of from 40.00 through 46.00; no more than 3 diopters of cornealcylinder; no pathology; age 15 through 50; and able to wear gaspermeable hard contact lens with reasonable comfort.

For each eye, a test kit of lenses was made with different diopters atand around the estimated best central touch fitting. The estimated bestcentral touch fit was determined based on the keratomer readings. Allkeratometer readings were obtained with a Bausch & Lomb keratometer.T.K. readings were obtained by having the patient look with the righteye nasally to the left horizontal "+" sign on the keratometer ring. Thepatients were examined either weekly or biweekly to determine the degreeof cornea reshaping. New lenses were central touch fit once a flatteningof the cornea of from 0.5 to 1.0 diopters was observed. On average, ittook from 1 to 2 weeks for a sufficient change in cornea shape to occurwhich required a new lens to be central touch fitted.

All of the lenses in the treatment series were were central touch fit toprovide gradual flattening of the cornea as the patient progressed fromthe first through the last set of lenses. The last lens in the seriesbecame a retainer lens to maintain the new cornea shape.

All of the patients in this study showed reshaping of the cornea andreduction in myopia within 90 days. Most of the eyes showed vision of20/30 or better.

Having thus described exemplary embodiments of the present invention, itshould be noted by those skilled in the art that the within disclosuresare exemplary only and that various other alternatives, adaptations andmodifications may be made within the scope of the present invention. Forexample, aspheric lenses with multiple tear zones and/or no peripheralzone may be utilized, if desired. Accordingly, the present invention isnot limited to the specific embodiments as illustrated herein, but isonly limited by the following claims.

What is claimed is:
 1. A method for treating a myopic eye comprising thesteps of:fitting a first contact lens to the cornea of a myopic eye,said first contact lens having an aspherically shaped posterior surfaceand wherein said first contact lens is central touch fit to said cornea;wearing said first contact lens for a sufficient time to flatten saidcornea to form a reshaped cornea; fitting a second contact lens to saidreshaped cornea, said second contact lens having an aspherically shapedposterior surface and wherein said second contact lens is central touchfit to said reshaped cornea; and wearing said second contact lens for asufficient time to further flatten said cornea to form a furtherreshaped cornea.
 2. A method for treating a myopic eye according toclaim 1 wherein the posterior surfaces of said first and second contactlenses have an aspheric eccentricity of between about 0.6 to 1.0.
 3. Amethod for treating a myopic eye according to claim 2 wherein theaspheric eccentricity of the posterior surfaces of said first and secondcontact lenses is about 0.8.
 4. A method for treating a myopic eyeaccording to claim 1 wherein said first and second contact lenses eachcomprise:an aspheric central zone having a central zone radius ofcurvature and a central zone periphery; wherein said radius of curvatureincreases from the center of said central zone to said periphery toprovide for multiple focusing of light passing through said cornealcontact lens into said eye; a tear zone located concentrically aroundsaid central zone and having a tear zone radius of curvature, whereinsaid tear zone radius of curvature is smaller than said central zoneradius of curvature; a peripheral zone located concentrically aroundsaid tear zone, said peripheral zone being integral with said tear zoneand having a peripheral zone radius of curvature wherein said peripheralzone radius of curvature is greater than or equal to said central zoneradius of curvature.
 5. A method for treating a myopic eye according toclaim 4 wherein the periphery of said aspheric central zone has adiameter of between about 6 to 20 millimeters.
 6. A method for treatinga myopic eye according to claim 4 wherein said peripheral zone comprisesa plurality of peripheral rings each having a different radius ofcurvature wherein the radius of curvature of said peripheral ringsincreases from the radially inward peripheral ring to the radiallyoutward peripheral ring.
 7. A method for treating a myopic eye accordingto claim 4 wherein the radius of curvature of said tear zone isaspheric.
 8. A method for treating a myopic eye according to claim 4wherein the radius of curvature of said peripheral zone is aspheric. 9.A method for treating a myopic eye according to claim 7 wherein theradius of curvature of said peripheral zone is aspheric.
 10. A methodfor treating a myopic eye according to claim 1 wherein said firstcontact lens is worn for a sufficient time to cause a 0.5 to 1.0 diopterchange in the central touch fitting of said cornea.
 11. A method fortreating a myopic eye according to claim 1 wherein said first contactlens is worn for about 1 to 2 weeks.